The present invention relates generally to an electric motor assembly which includes an air-ventilated electric motor, and more particularly to such an assembly which also includes an external muffler bank (i.e., an external muffler array) for attenuating electric motor ventilation noise.
Electric motors include large electric motors, such as industrial electric motors and transit vehicle electric motors, which must be air cooled. Such air-ventilated electric motors typically have fan blades attached to the rotor shaft inside the motor housing to pull cooling air across the rotor and through the stator windings or have an independent cooling fan outside the motor housing to push cooling air through the motor housing and across the rotor and through the stator windings contained therein. Such ventilation system of a large electric motor creates excessive broadband noise from the flow turbulence and excessive tonal noise from the fan blade passage and the rotor bar passage which poses a health and safety issue in both industrial settings and urban transit applications.
A known noise attenuation technique is to employ an integral silencer disposed within the motor housing of an air-ventilated electric motor having fan blades, such silencer including an expansion chamber and a resonating chamber which are two reactive muffler acoustic elements. Some electric-motor applications provide little space to expand the motor housing to include an integral silencer. What is needed is a noise attenuation technique for an air-ventilated electric motor which allows for greater flexibility in muffler design (i.e., in the size, shape, location, and tuning of the muffler acoustic elements) for maximum acoustic attenuation while minimizing any additional flow resistance caused by the presence of the muffler acoustic elements.